Added deletion of existing VOs in the SetUp() method of CatalogueTest

The added codes appeared in production (with the CASTOR Nameserver)
during a network incident with the Oracle Clusterware.

Corrected helgrind errors by adding mutexes for multithread access to RecallReportPacker attributes.

If the disk threads are not finished after the TapeReadSingleThread finished, the status of the drive will be "DrainingToDisk"
This removed a RecallReportPacker exception when trying to release disk space reservation for backpressure

In DriveState::addDiskSpaceReservation and substractDiskSpaceReservation, use a reference to the mutable_disk_space_reservations item

migration: made update of pre-existing storage classes consistent to the update of tape pools, that is take the latest CASTOR metadata as valid

upgrading to eos 4.7.0-20200221155245git994c2f1 that adds eosreports for failed transfers and fix xrootd query prepare on_tape bug

of the script after validation in castorpps

Added UNIQUE constraint on STORAGE_CLASS_NAME and removed the the UNIQUE constraint on DISK_INSTANCE_NAME and STORAGE_CLASS_NAME